Conventionally, an embroidery frame has been used that retains an embroidery workpiece cloth in a stretched manner by an outer frame and an inner frame. Such embroidery frame clamps the workpiece cloth between an inner peripheral surface of the outer frame and an outer peripheral surface of the inner frame. Therefore, the problem with such embroidery frame is the formation of creases on the portion clamped by the outer frame and the inner frame when the workpiece cloth is removed from between the outer and inner frames. Also, the outer frame is equipped with a clamping screw for adjusting the size of the outer frame. Therefore, whenever the workpiece cloth is attached to or detached from the embroidery frame, the clamping screw needs to be operated in order to adjust the size of the outer frame, which provides poor workability.
On the other hand, embroidery frames have been suggested in which the workpiece cloth is retained between the upper and lower frames. In such embroidery frames, the workpiece cloth is less prone to creasing, since the workpiece cloth is clamped between the lower surface of the upper frame and the upper surface of the lower frame. However, because the embroidery frame is constructed to simply press the upper frame against the lower frame, sufficient tension cannot be applied to the workpiece cloth clamped between the upper and lower frames. Also, embroidery frames constructed by outer and inner frames have better cloth retainability than embroidery frames constructed by upper and lower frames. Thus, during the sewing process, the workpiece cloth is gradually pulled inward by the thread tension of embroidery patterns, leading to pattern distortion and impairment of sewing quality.
Such being the case, embroidery frames equipped with an auxiliary frame that further downwardly press the workpiece cloth clamped between the upper and lower frames have been reduced to practice. For example, JP-A-8-243280 discloses a workpiece cloth-retaining frame of a clamp type provided with a base frame (lower frame), a first presser frame (upper frame), a second presser frame (auxiliary frame), a first clamp mechanism that presses the upper frame against the lower frame, and a second clamp mechanism that presses the auxiliary frame against the lower frame. The lower frame is provided with a first receiving portion, an elevated portion formed as an elevated stage in the inner peripheral portion of the first receiving portion, and a second receiving portion formed as a lowered stage in the inner peripheral portion of the elevated portion. After fixing the workpiece cloth to the lower frame by pressing the upper frame against the first receiving portion of the lower frame by the first clamp mechanism, when the auxiliary frame is pressed against the second receiving portion of the lower frame by the second clamp mechanism, the auxiliary frame downwardly presses the workpiece cloth in uneven levels in the inner peripheral portion of the upper frame. Thus, the workpiece cloth is retained in a sufficiently stretched state.
However, a clamp mechanism that presses the auxiliary frame to the workpiece cloth is required in addition to the clamp mechanism that presses the upper frame against the lower frame in the above constructed embroidery frame. This leads to an increase in the number of parts, consequently increasing the complexity as well as the weight of the embroidery frame.